Recovering now :-) Stuck at some exercises I found on the net and seems to paying dividends. 10 mile fell run a week last Friday (back started to ache but hamstring/piriformis stretches stopped it), followed up by 8 mile trail run and 4.5 fastish fell run last week. I did end up seeing another physio from running club who foun nothing untoward - just needed to persevere with the exercises